The Bacillus subtilis RNase P holoenzyme contains two RNase P RNA and two RNase P protein subunits

Ribonuclease P (RNase P) catalyzes the 5' maturation of precursor tRNA transcripts and, in bacteria, is composed of a catalytic RNA and a protein, We investigated the oligomerization state and the shape of the RNA alone and the holoenzyme of Bacillus subtilis RNase P in the absence of substrate by synchrotron small-angle X-ray scattering and affinity retention. The B, subtilis RNase P RNA alone is a monomer; however, the scattering profile changes upon the addition of monovalent ions, possibly suggesting different interdomain angles, To our surprise, the X-ray scattering data combined with the affinity retention results indicate that the holoenzyme contains two RNase P RNA and two RNase P protein molecules. We propose a structural model of the holoenzyme with a symmetrical arrangement of the two RNA subunits, consistent with the X-ray scattering results, This (P RNA)(2)(P protein)(2) complex likely binds substrate differently than the conventional (P RNA)(1)(P protein)(1) complex; therefore, the function of the B. subtilis RNase P holoenzyme may be more diverse than previously thought. These revisions to our knowledge of the RNase P holoenzyme suggest a more versatile role for proteins in ribonucleoprotein complexes.